In two breakthrough developments, NASA scientists have
beamed microwaves and laser energy to "fill" lightweight sails in
laboratory demonstrations of how these technologies might provide
propulsion for interstellar exploration.

The sails used in the microwave experiment were actually
driven to liftoff and flight, while the laser-driven sails
achieved horizontal movement.

"These are really two giant steps forward," said Henry
Harris, task manager for the microwave levitation and laser
experiments at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
"These results would not have been possible without newly
developed ultralight, high-temperature sail materials and beamed-
energy propulsion methods."

Future spacecraft that explore the depths of space will need
to be very lightweight and be propelled by a reliable source of
energy. Solar sails and microwave- and laser-beamed sails meet
this requirement, with minimal weight since in the first case the
"engine" is the Sun, while in the latter two the engine is left
at the point of origin. The sails are driven by photons,
particles of energy in which sunlight and other forms of
electromagnetic radiation are emitted. By use of a remote laser
or microwave source, beamed energy can be directed toward a space
sail. In space, the laser or microwave source may be provided by
a satellite or other type of spacecraft.

The microwave-beamed sail experiment was conducted in a
vacuum chamber at JPL, while the laser-driven experiment took
place in another vacuum chamber at Wright-Patterson Air Force
Base in Ohio. Both of these experiments appear to be firsts.

"Accelerations of several times the force of gravity were
observed during the microwave tests," said Dr. James Benford,
project director and president, Microwave Sciences, Inc.,
Lafayette, Calif. "In one case, the sail flew two feet in
response to the high acceleration."

About 10 kilowatts of microwave power were beamed to the
sails. Analysis of data is underway to isolate the photon
pressure effect from other possible causes of sail movement. In
the other tests, laser powers from 7.9 to 13.9 kilowatts were
directed to the sails. Photon thrust was calculated from
movements of the sails, which were mounted on pendulums. Future
research will fine-tune the scientific understanding of flight
using photon pressure.

Sails for both experiments were made of carbon-carbon
microtruss fabric and were provided by Dr. Timothy Knowles,
Energy Science Laboratory, Inc., San Diego, Calif. This very
light but stiff fabric can withstand high temperatures that are
typical of flight-level power densities.

"These experiments are the first known measurements of laser
photon thrust performance using lightweight sails that are
candidates for spaceflight," said Dr. Leik Myrabo, associate
professor at Rensselaer Polytechnic Institute, Troy, N.Y.

Both Benford and Myrabo are lead authors of papers
describing the experiments. "Experimental Investigation of Laser-
Pushed Light Sails in A Vacuum," by Myrabo, was presented June 2
during the Advanced Propulsion Conference at JPL. Benford's
paper, "Microwave Beam-Driven Propulsion Experiments for High-
Speed Space Exploration," was presented at EuroEM 2000, held in
Edinburgh, Scotland, May 30-June 2 and also at the JPL
conference. Knowles and Harris are among the co-authors on both
papers. Harris is also co-investigator on the microwave
experiment.

Energy Science Laboratories Inc. holds the patent on the
sail materials used in these tests. JPL has overall
responsibility for NASA's interstellar missions, while NASA's
Marshall Space Flight Center, Huntsville, Ala., is responsible
for developing transportation systems for the missions. The laser
experiment was conducted in the Laser Hardened Materials
Evaluation Laboratory II at Wright-Patterson Air Force Base.

JPL manages Interstellar Technology Development for NASA's
Office of Space Sciences. JPL is managed for NASA by the
California Institute of Technology in Pasadena.